Method and apparatus for link configuration and routing of relay system

ABSTRACT

An operation method of a first terminal may include: configuring a Uu access link with a base station, and receiving a first message from the base station, the first message including a relay RNTI for identifying the first terminal, a node address of the base station, and a RAP entity ID for identifying a RAP entity configured for the first terminal; configuring a relay link with a second terminal when communication with the base station is disconnected; requesting link switching by transmitting to the base station a second message via the second terminal, the second message including the relay RNTI, node address, and RAP entity ID; and receiving a response to the second message from the base station via the second terminal, and switching a link with the base station from the Uu access link to the relay link.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Korean Patent Applications No.10-2020-0137886 filed on Oct. 22, 2020 and No. 10-2021-0087810 filed onJul. 5, 2021 with the Korean Intellectual Property Office (KIPO), theentire contents of which are hereby incorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to a technique for link configuration androuting of a relay system, and more particularly, to a technique forlink configuration and routing of a relay system that continuescommunication service via a relay when communication with a base stationis disconnected.

2. Description of Related Art

In order to process wireless data that increases rapidly aftercommercialization of the fourth generation (4G) communication system(e.g., long term evolution (LTE) communication system or LTE-Advanced(LTE-A) communication system), a fifth generation (5G) communicationsystem (e.g., new radio (NR) communication system) using not only afrequency band (e.g., frequency band of 6 GHz or below) of the 4Gcommunication system but also a frequency band (e.g., frequency band of6 GHz or above) higher than the frequency band of the 4G communicationsystem is being considered. The 5G communication system may supportenhanced Mobile BroadBand (eMBB), Ultra-Reliable and Low LatencyCommunication (URLLC), and massive Machine Type Communication (mMTC).

Meanwhile, among the communication systems, a millimeter wave-basedmobile communication system may provide a broadband service usingbeamforming. In the millimeter wave-based mobile communication system, aterminal may frequently experience communication service blockages dueto obstacles such as trees, traffic signs, and automobiles according tomillimeter wave frequency characteristics. In such the case, if anadjacent terminal performs a role of a relay, service continuity may beguaranteed to the terminal (i.e., remote terminal) whose communicationservice is disconnected. To this end, the adjacent terminal may performforwarding of relay traffic of the terminal whose communication serviceis disconnected. As such, in order for the adjacent terminal to performforwarding of relay traffic, a signaling procedure for link switchingand a signaling procedure for registering, changing, and releasingrouting information for the data forwarding may be required.

SUMMARY

Accordingly, exemplary embodiments of the present disclosure aredirected to providing a method and an apparatus for link and routingconfiguration of a relay system, which can provide a procedure of linkswitching for an adjacent terminal to perform forwarding of relaytraffic, and a procedure of registering, changing, and releasing routinginformation.

According to a first exemplary embodiment of the present disclosure, anoperation method of a first terminal in a communication system maycomprise: configuring a Uu access link with a base station, andreceiving a first message from the base station, the first messageincluding a relay radio network temporary identifier (RNTI) foridentifying the first terminal, a node address of the base station, anda relay adaptation protocol (RAP) entity identifier (ID) for identifyinga RAP entity configured for the first terminal; configuring a relay linkwith a second terminal when communication with the base station isdisconnected; requesting link switching by transmitting to the basestation a second message via the second terminal, the second messageincluding the relay RNTI, the node address, and the RAP entity ID; andreceiving a response to the second message from the base station via thesecond terminal, and switching a link with the base station from the Uuaccess link to the relay link.

The requesting of the link switching may comprise: generating a firstmessage authentication code for integrity (MAC-I) by processingintegrity protection based on the relay RNTI, the node address, and theRAP entity; generating the second message including the relay RNTI, thenode address, the RAP entity, and the first MAC-I information; andrequesting the link switching by transmitting the second message to thebase station via the second terminal.

The receiving of the response and the switching of the link maycomprise: receiving the response to the second message including therelay RNTI, the node address, and a second MAC-I from the base stationvia the second terminal; generating a third MAC-I by processingintegrity protection based on the relay RNTI and the node address; andin response to determining that the third MAC-I and the second MAC-Imatch, switching the link with the base station from the Uu access linkto the relay link, and transmitting uplink data through the relay link.

The operation method may further comprise, after the configuring of therelay link, configuring a routing table entry based on the node address,the RAP entity ID, and a first branch node address received from thesecond terminal in the configuring of the relay link; and in response toreceiving the response to the second message from the base station,activating the routing table entry.

The operation method may further comprise: receiving, from the secondterminal, a third message requesting update of the routing table entry,the third message including a second branch node address; and updatingthe routing table entry by reflecting the second branch node address.

The operation method may further comprise: starting a timer aftertransmitting the second message; and releasing the relay link if theresponse to the second message is not received within a waiting timedefined by the timer.

According to a second exemplary embodiment of the present disclosure, anoperation method of a second terminal in a communication system maycomprise: configuring a relay link with a first terminal; receiving,from the first terminal, a second message requesting link switching, andtransmitting the second message to a second base station, the secondmessage including a root node address that is a node address of a firstbase station to which the first terminal is connected, and a relayadaptation protocol (RAP) entity ID for identifying a RAP entity for thefirst terminal configured in the first base station; configuring arouting table entry based on the root node address, the RAP entity ID,and a node address of the second base station; receiving a third messagefrom the second base station in response to the second message, andtransmitting the third message to the first terminal, the third messageincluding the root node address and the RAP entity ID; and activatingthe routing table entry.

The configuring of the routing table entry may comprise: receiving thenode address of the second base station from the second base station;detecting the root node address and the RAP entity ID in the secondmessage; and configuring the routing table entry based on the root nodeaddress, the RAP entity ID, and the node address of the second basestation.

The activating of the routing table entry may comprise: searching arouting table based on the root node address and the RAP entity ID ofthe third message; and activating the routing table entry when therouting table entry associated with the root node address and the RAPentity ID is retrieved in the routing table.

The operation method may further comprise: receiving, from the firstterminal, a fourth message including the root node address and the RAPentity ID; searching a routing table based on the root node address andthe RAP entity ID of the fourth message; and when the routing tableentry associated with the root node address and the RAP entity ID isretrieved in the routing table, transmitting the fourth message based onthe retrieved routing table entry.

The operation method may further comprise: receiving a node address of athird base station from the third base station by being connected to thethird base station through inter-cell movement; and updating the routingtable entry by reflecting the node address of the third base stationreceived from the third base station.

According to a third exemplary embodiment of the present disclosure, anoperation method of a base station in a communication system maycomprise: transmitting a first message to a first terminal when thefirst terminal configures a Uu access link with the base station bybeing connected to the base station, the first message including a relayradio network temporary identifier (RNTI) for identifying the firstterminal, a node address of the base station, and a relay adaptationprotocol (RAP) entity identifier (ID) for identifying a RAP entityconfigured for the first terminal; receiving, from the first terminal, asecond message requesting link switching via a second terminal, thesecond message including the relay RNTI, the root node address, and theRAP entity ID; identifying the Uu access link connected with the firstterminal by using the relay RNTI and the RAP entity ID according to thesecond message requesting link switching, and switching a link with thefirst terminal from the Uu access link to a relay link via the secondterminal; and transmitting, to the first terminal, a third messageinforming completion of the link switching via the second terminal, thethird message including the relay RNTI, the node address, and the RAPentity ID.

The switching of the link may comprise: identifying the first terminalbased on the relay RNTI of the second message; identifying the Uu accesslink corresponding to the first terminal by using the RAP entity ID; andswitching the link with the first terminal from the identified Uu accesslink to the relay link via the second terminal.

The operation method may further comprise: configuring a routing tableentry based on the node address and the RAP entity ID upon receiving thefirst message; performing an integrity check on the second message; andactivating the routing table entry if the integrity check is successful.

According to the exemplary embodiments of the present disclosure, theterminal relay system may provide a procedure of link switching from aUu access link to a relay link for a terminal whose communicationservice is disconnected. In addition, according to the exemplaryembodiments of the present disclosure, the terminal relay system mayprovide a procedure of registering, changing, and releasing routinginformation for data forwarding of a terminal whose communicationservice is disconnected. In addition, according to the exemplaryembodiments of the present disclosure, by providing a terminal relaysignaling procedure, a terminal whose communication service isdisconnected due to an obstacle or the like may transmit and receivedata using a relay function of an adjacent terminal. In addition,according to the exemplary embodiments of the present disclosure, byproviding a terminal relay signaling procedure, a terminal not capableof transmitting and receiving data outside a cell coverage may transmitand receive data using a relay function of an adjacent terminal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating a first exemplary embodimentof a communication system.

FIG. 2 is a block diagram illustrating a first exemplary embodiment of acommunication node constituting a communication system.

FIG. 3 is a conceptual diagram illustrating a first exemplary embodimentof a terminal relay system.

FIG. 4 is a conceptual diagram illustrating a second exemplaryembodiment of a terminal relay system.

FIG. 5 is a diagram of a protocol stack structure of a terminal relaysystem according to a first exemplary embodiment.

FIG. 6 is a block diagram illustrating a first exemplary embodiment ofentities of a terminal relay system.

FIG. 7 is a conceptual diagram illustrating a method of assigningaddresses and identifiers to a base station and entities of the basestation.

FIG. 8 is a sequence chart illustrating a first exemplary embodiment ofa method for configuring a link between a remote terminal and a basestation.

FIG. 9 is a sequence chart illustrating a first exemplary embodiment ofa method for configuring a link between a remote terminal and a relayterminal.

FIG. 10 is a sequence chart illustrating a first exemplary embodiment ofa method for switching a link with a remote terminal from a Uu accesslink to a relay link.

FIG. 11 is a flowchart illustrating a first exemplary embodiment of anoperation method of an RRC entity of a remote terminal.

FIG. 12 is a flowchart illustrating a first exemplary embodiment of alink switching method of an RRC entity of a base station.

FIG. 13 is a flowchart illustrating a first exemplary embodiment of alink switching method of an RRC entity of a remote terminal.

FIG. 14 is a flowchart illustrating a first exemplary embodiment of amethod for configuring routing information performed by a remoteterminal.

FIG. 15 is a flowchart illustrating a first exemplary embodiment of amethod for configuring routing information performed by a RAP entity ofa relay terminal.

FIG. 16 is a flowchart illustrating a first exemplary embodiment of amethod for data relaying performed by a relay terminal.

FIG. 17 is a conceptual diagram illustrating a third exemplaryembodiment of a terminal relay system.

FIG. 18 is a flowchart illustrating a first exemplary embodiment of amethod of changing a branch node address performed by a relay terminal.

FIG. 19 is a flowchart illustrating a first exemplary embodiment of amethod for changing a branch node address performed by a remoteterminal.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present disclosure are disclosed herein. However,specific structural and functional details disclosed herein are merelyrepresentative for purposes of describing embodiments of the presentdisclosure. Thus, embodiments of the present disclosure may be embodiedin many alternate forms and should not be construed as limited toembodiments of the present disclosure set forth herein.

Accordingly, while the present disclosure is capable of variousmodifications and alternative forms, specific embodiments thereof areshown by way of example in the drawings and will herein be described indetail. It should be understood, however, that there is no intent tolimit the present disclosure to the particular forms disclosed, but onthe contrary, the present disclosure is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of thepresent disclosure. Like numbers refer to like elements throughout thedescription of the figures.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present disclosure. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(i.e., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this present disclosure belongs.It will be further understood that terms, such as those defined incommonly used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the relevant artand will not be interpreted in an idealized or overly formal senseunless expressly so defined herein.

Hereinafter, exemplary embodiments of the present disclosure will bedescribed in greater detail with reference to the accompanying drawings.In order to facilitate general understanding in describing the presentdisclosure, the same components in the drawings are denoted with thesame reference signs, and repeated description thereof will be omitted.

FIG. 1 is a conceptual diagram illustrating a first exemplary embodimentof a communication system.

Referring to FIG. 1 , a communication system 100 may comprise aplurality of communication nodes 110-1, 110-2, 110-3, 120-1, 120-2,130-1, 130-2, 130-3, 130-4, 130-5, and 130-6. Here, the communicationsystem may be referred to as a ‘communication network’. Each of theplurality of communication nodes may support at least one communicationprotocol. For example, each of the plurality of communication nodes 110to 130 may support communication protocols defined in the 3rd generationpartnership project (3GPP) technical specifications (e.g., LTEcommunication protocol, LTE-A communication protocol, NR communicationprotocol, or the like). The plurality of communication nodes 110 to 130may support code division multiple access (CDMA) based communicationprotocol, wideband CDMA (WCDMA) based communication protocol, timedivision multiple access (TDMA) based communication protocol, frequencydivision multiple access (FDMA) based communication protocol, orthogonalfrequency division multiplexing (OFDM) based communication protocol,filtered OFDM based communication protocol, cyclic prefix OFDM (CP-OFDM)based communication protocol, discrete Fourier transform-spread-OFDM(DFT-s-OFDM) based communication protocol, orthogonal frequency divisionmultiple access (OFDMA) based communication protocol, single carrierFDMA (SC-FDMA) based communication protocol, non-orthogonal multipleaccess (NOMA) based communication protocol, generalized frequencydivision multiplexing (GFDM) based communication protocol, filter bandmulti-carrier (FBMC) based communication protocol, universal filteredmulti-carrier (UFMC) based communication protocol, space divisionmultiple access (SDMA) based communication protocol, or the like. Eachof the plurality of communication nodes may have the followingstructure.

FIG. 2 is a block diagram illustrating a first exemplary embodiment of acommunication node constituting a communication system.

Referring to FIG. 2 , a communication node 200 may comprise at least oneprocessor 210, a memory 220, and a transceiver 230 connected to thenetwork for performing communications. Also, the communication node 200may further comprise an input interface device 240, an output interfacedevice 250, a storage device 260, and the like. Each component includedin the communication node 200 may communicate with each other asconnected through a bus 270. However, each of the components included inthe communication node 200 may be connected not to the common bus 270but to the processor 210 through an individual interface or anindividual bus. For example, the processor 210 may be connected to atleast one of the memory 220, the transceiver 230, the input interfacedevice 240, the output interface device 250, and the storage device 260through dedicated interfaces.

The processor 210 may execute a program stored in at least one of thememory 220 and the storage device 260. The processor 210 may refer to acentral processing unit (CPU), a graphics processing unit (GPU), or adedicated processor on which methods in accordance with embodiments ofthe present disclosure are performed. Each of the memory 220 and thestorage device 260 may be constituted by at least one of a volatilestorage medium and a non-volatile storage medium. For example, thememory 220 may comprise at least one of read-only memory (ROM) andrandom access memory (RAM).

Referring again to FIG. 1 , the communication system 100 may comprise aplurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2, and aplurality of terminals 130-1, 130-2, 130-3, 130-4, 130-5, and 130-6.Each of the first base station 110-1, the second base station 110-2, andthe third base station 110-3 may form a macro cell, and each of thefourth base station 120-1 and the fifth base station 120-2 may form asmall cell. The fourth base station 120-1, the third terminal 130-3, andthe fourth terminal 130-4 may belong to the cell coverage of the firstbase station 110-1. Also, the second terminal 130-2, the fourth terminal130-4, and the fifth terminal 130-5 may belong to the cell coverage ofthe second base station 110-2. Also, the fifth base station 120-2, thefourth terminal 130-4, the fifth terminal 130-5, and the sixth terminal130-6 may belong to the cell coverage of the third base station 110-3.Also, the first terminal 130-1 may belong to the cell coverage of thefourth base station 120-1, and the sixth terminal 130-6 may belong tothe cell coverage of the fifth base station 120-2.

Here, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1,and 120-2 may be referred to as NodeB (NB), evolved NodeB (eNB), gNB,advanced base station (ABS), high reliability-base station (HR-BS), basetransceiver station (BTS), radio base station, radio transceiver, accesspoint (AP), access node, radio access station (RAS), mobile multihoprelay-base station (MMR-BS), relay station (RS), advanced relay station(ARS), high reliability-relay station (HR-RS), home NodeB (HNB), homeeNodeB (HeNB), road side unit (RSU), radio remote head (RRH),transmission point (TP), transmission and reception point (TRP), relaynode, or the like. Each of the plurality of terminals 130-1, 130-2,130-3, 130-4, 130-5, and 130-6 may be referred to as user equipment(UE), terminal equipment (TE), advanced mobile station (AMS), highreliability-mobile station (HR-MS), terminal, access terminal, mobileterminal, station, subscriber station, mobile station, portablesubscriber station, node, device, on-board unit (OBU), or the like.

Each of the plurality of communication nodes 110-1, 110-2, 110-3, 120-1,120-2, 130-1, 130-2, 130-3, 130-4, 130-5, and 130-6 may support cellularcommunication (e.g., LTE, LTE-Advanced (LTE-A), etc.) defined in the 3rdgeneration partnership project (3GPP) specification. Each of theplurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 mayoperate in the same frequency band or in different frequency bands. Theplurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may beconnected to each other via an ideal backhaul link or a non-idealbackhaul link, and exchange information with each other via the ideal ornon-ideal backhaul. Also, each of the plurality of base stations 110-1,110-2, 110-3, 120-1, and 120-2 may be connected to the core networkthrough the ideal backhaul link or non-ideal backhaul link. Each of theplurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 maytransmit a signal received from the core network to the correspondingterminal 130-1, 130-2, 130-3, 130-4, 130-5, or 130-6, and transmit asignal received from the corresponding terminal 130-1, 130-2, 130-3,130-4, 130-5, or 130-6 to the core network.

Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and120-2 may support OFDMA-based downlink (DL) transmission, andSC-FDMA-based uplink (UL) transmission. In addition, each of theplurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 maysupport a multi-input multi-output (MIMO) transmission (e.g.,single-user MIMO (SU-MIMO), multi-user MIMO (MU-MIMO), massive MIMO, orthe like), a coordinated multipoint (CoMP) transmission, a carrieraggregation (CA) transmission, a transmission in unlicensed band, adevice-to-device (D2D) communication (or, proximity services (ProSe)),an Internet of Things (IoT) communication, a dual connectivity (DC), orthe like. Here, each of the plurality of terminals 130-1, 130-2, 130-3,130-4, 130-5, and 130-6 may perform operations corresponding to theoperations of the plurality of base stations 110-1, 110-2, 110-3, 120-1,and 120-2 (i.e., the operations supported by the plurality of basestations 110-1, 110-2, 110-3, 120-1, and 120-2).

For example, the second base station 110-2 may transmit a signal to thefourth terminal 130-4 in the SU-MIMO manner, and the fourth terminal130-4 may receive the signal from the second base station 110-2 in theSU-MIMO manner. Alternatively, the second base station 110-2 maytransmit a signal to the fourth terminal 130-4 and fifth terminal 130-5in the MU-MIMO manner, and the fourth terminal 130-4 and fifth terminal130-5 may receive the signal from the second base station 110-2 in theMU-MIMO manner. Each of the first base station 110-1, the second basestation 110-2, and the third base station 110-3 may transmit a signal tothe fourth terminal 130-4 in the CoMP transmission manner, and thefourth terminal 130-4 may receive the signal from the first base station110-1, the second base station 110-2, and the third base station 110-3in the CoMP manner. Also, each of the plurality of base stations 110-1,110-2, 110-3, 120-1, and 120-2 may exchange signals with thecorresponding terminals 130-1, 130-2, 130-3, 130-4, 130-5, or 130-6which belongs to its cell coverage in the CA manner. Each of the basestations 110-1, 110-2, and 110-3 may control D2D communications betweenthe fourth terminal 130-4 and the fifth terminal 130-5, and thus thefourth terminal 130-4 and the fifth terminal 130-5 may perform the D2Dcommunications under control of the second base station 110-2 and thethird base station 110-3.

Meanwhile, a millimeter wave-based mobile communication system mayprovide a broadband service using beamforming. In the millimeterwave-based mobile communication system, a terminal may frequentlyexperience communication service blockages due to obstacles such astrees, traffic signs, and automobiles according to millimeter wavefrequency characteristics. In such the case, if an adjacent terminalperforms a role of a relay, service continuity may be guaranteed to theterminal whose communication service is disconnected.

FIG. 3 is a conceptual diagram illustrating a first exemplary embodimentof a terminal relay system.

Referring to FIG. 3 , a terminal relay system may include a base station310, a first terminal 321, a second terminal 322, and a third terminal323. The first terminal 321 and the second terminal 322 may be locatedin a communication service coverage of the base station 310, and thethird terminal 323 may be located out of the communication servicecoverage of the base station 310. Here, the third terminal 323 may moveout of the communication service coverage of the base station 310 due toa movement therefrom. As such, when the third terminal 323 is locatedout of the communication service coverage of the base station 310, thethird terminal 323 may access the base station 310 via the secondterminal 322 to perform data transmission and reception with the basestation 310. In this case, the second terminal 322 may relaycommunication between the base station 310 and the third terminal 323.On the other hand, since the first terminal 321 is located in thecommunication service coverage of the base station 310, the firstterminal 321 may directly access the base station 310 to transmit andreceive data to and from the base station 310. In this case, the firstterminal 321 may enter a communication disconnected (e.g., blockage)state in which data cannot be transmitted/received to and from the basestation 310 due to an obstacle or the like. In this case, the firstterminal 321 may access the base station 310 via the second terminal 322to transmit and receive data to and from the base station 310.Accordingly, the second terminal 322 may relay communication between thebase station 310 and the first terminal 321. When a communicationdisconnected state occurs in which data cannot be directlytransmitted/received to and from the base station 310 due to an obstacleor the like as in the case of the first terminal 321, the terminal relaysystem may use the adjacent second terminal 322 as a relay so that thefirst terminal 321 continues to perform data transmission and receptionwith the first base station 310. In addition, when a terminal is unableto transmit and receive data to and from the base station 310 outsidethe cell coverage as in the case of the third terminal 323, the terminalrelay system may use the adjacent second terminal 322 as a relay so thatthe third terminal 323 continues to perform data transmission andreception with the first base station 310.

FIG. 4 is a conceptual diagram illustrating a second exemplaryembodiment of a terminal relay system.

Referring to FIG. 4 , a terminal relay system may include a first basestation 411, a second base station 412, a first terminal 421, and asecond terminal 422. The first terminal 421 may be located in acommunication service coverage of the first base station 412, and thesecond terminal 422 may be located in a communication service coverageof the second base station 412. As such, since the first terminal 421 islocated in the communication service coverage of the first base station411, the first terminal 421 may directly access the first base station411 to transmit and receive data to and from the first base station 411.In addition, since the second terminal 422 is located in thecommunication service coverage of the second base station 412, thesecond terminal 422 may directly access the second base station 412 totransmit and receive data to and from the second base station 412. Fromsuch the state, the first terminal 421 may enter a communicationdisconnected state in which data cannot be transmitted and received toand from the first base station 411 due to an obstacle or the like. Inthis case, the first terminal 421 may access the first base station 411via the second terminal 422 and the second base station 412 to transmitand receive data to and from the first base station 411. In this case,the second terminal 422 may relay communication between the second basestation 412 and the first terminal 421. In addition, the second basestation 412 may relay communication between the first base station 411and the second terminal 422. As such, even when the second terminal 422adjacent to the first terminal 421 is located out of the communicationservice coverage of the first base station 411 providing a communicationservice to the first terminal 421, the terminal relay system may enablecontinuous data transmission/reception between the first base station411 and the first terminal 421 via the second base station 412 providinga communication service to the second terminal 422.

FIG. 5 is a diagram of a protocol stack structure of a terminal relaysystem according to a first exemplary embodiment.

Referring to FIG. 5 , a protocol stack structure of the terminal relaysystem may include a protocol stack structure of a base station 510, aprotocol stack structure of a relay terminal 520, and a protocol stackstructure of a remote terminal 530.

Here, the protocol stack structure of the base station 510 may include afirst service data adaptation protocol (SDAP) layer 511, a first packetdata convergence protocol (PDCP) layer 512, a first relay adaptationprotocol (RAP) layer 513, a first radio link control (RLC) layer 514-1,a second RLC layer 514-2, a first medium access control (MAC) layer515-1, a second MAC layer 515-2, a first physical (PHY) layer 516-1, anda second PHY layer 516-2. In the protocol stack structure of the basestation 510, the first SDAP layer 511, the first PDCP layer 512, thefirst RLC layer 514-1, the first MAC layer 515-1, and the first PHYlayer 516-1 may support direct transmission and reception of datathrough a Uu access link of a Uu interface before the remote terminal530 enters a communication disconnected state. In addition, when theremote terminal 530 enters a communication disconnected state, the firstSDAP layer 511, the first PDCP layer 512, the first RAP layer 513, thesecond RLC layer 514-2, the second MAC layer 515-2, and the second PHYlayer 516-2 in the protocol stack structure of the base station 510 maysupport communication through a Uu access link 540 of a Uu interfacewith the relay terminal 520, thereby transmitting and receiving data toand from the remote terminal 530 via the relay terminal 520.

Meanwhile, the protocol stack structure of the relay terminal 520 mayinclude a second RAP layer 521-1, a third RAP layer 521-2, a third RLClayer 522-1, a fourth RLC layer 522-2, a third MAC layer 523-1, a fourthMAC layer 523-2, a third PHY layer 524-1, and a fourth PHY layer 524-2.In the protocol stack structure of the relay terminal 520, the secondRAP layer 521-1, the third RLC layer 522-1, the third MAC layer 523-1,and the first PHY layer 524-1 may support communication with the basestation 510 through the Uu access link 540 of the Uu interface. Incontrast, in the protocol stack structure of the relay terminal 520, thethird RAP layer 521-2, the fourth RLC layer 522-2, the fourth MAC layer523-2, and the fourth PHY layer 524-2 may support communication with theremote terminal 530 through a sidelink or a relay link 550.

In addition, the protocol stack structure of the remote terminal 530 mayinclude a second SDAP layer 531, a second PDCP layer 532, a fourth RAPlayer 533, a fifth RLC layer 534-1, a sixth RLC layer 534-2, a fifth MAClayer 535-1, a sixth MAC layer 535-2, a fifth PHY layer 536-1, and asixth PHY layer 536-2. In the protocol stack structure of the remoteterminal 530, the second SDAP layer 531, the second PDCP layer 532, thefifth RLC layer 534-1, the fifth MAC layer 535-1, and the fifth PHYlayer 536-1 may support direct data transmission and reception with thebase station 510 through a Uu access link before the remote terminalenters a communication disconnected state. In contrast, in the protocolstack structure of the remote terminal 530, the second SDAP layer 531,the second PDCP layer 532, the fourth RAP layer 533, the sixth RLC layer534-2, the sixth MAC The layer 535-2, and the sixth PHY layer 536-2 maysupport communication with the relay terminal 520 through the sidelinkor a relay link 550 when the remote terminal 530 enters a communicationdisconnected state.

As described above, in the terminal relay system, the first RAP layer513 may be added in the protocol stack structure of the base station 510as a lower layer of the first PDCP layer 512 so that the base station510 communicates with the relay terminal 520 to transmit and receivedata to and from the remote terminal 530, and the second RLC layer514-2, the second MAC layer 515-2, the second PHY layer 516-2 may beprovided to support the added first RAP layer 513. In addition, in theterminal relay system, the second RAP layer 521-1 may be added in theprotocol stack structure of the relay terminal 520 so that the relayterminal 520 communicates with the base station 510 to transmit andreceive data to and from the base station 510, and the third RLC layer522-1, the third MAC layer 523-1, and the third PHY layer 524-1 may beprovided to support the added second RAP layer 521-1.

In addition to these, in the terminal relay system, the third RAP layer521-2 may be added in the protocol stack structure of the relay terminal520 so that the relay terminal 520 communicates with the remote terminal530 to transmit and receive data to and from the remote terminal 530,and the fourth RLC layer 522-2, the fourth MAC layer 523-2, and thefourth PHY layer 524-2 may be provided to support the added third RAPlayer 521-2. Further, in the terminal relay system, the fourth RAP layer533 may be added in the protocol stack structure of the remote terminal530 as a lower layer of the second PDCP layer 532 so that the remoteterminal 530 can communicate with the relay terminal 520 to transmit andreceive data to and from the relay terminal 520, and the sixth RLC layer534-2, the sixth MAC layer 535-2, and the sixth PHY layer 536-2 may beprovided to support the added fourth RAP layer 533. As described above,in order to support the relay function, the first RAP layer 513 and thefourth RAP layer 533 may be located between the PDCP layers 512 and 532and the RLC layers 514-1, 514-2, 534-1, and 534-2 according to thegeneral protocol stack structure including the SDAP layers 511 and 531,PDCP layers 512 and 532, RLC layers 514-1, 514-2, 534-1, and 534-2, andMAC layer 515-1, 515-2, 535-1, and 535-2.

As described above, the terminal relay system may use a plurality of RAPlayers 513, 521-1, 521-2, and 533 to provide relay to the base station510 through the relay terminal 520 adjacent to the remote terminal 530.The base station 510 and the remote terminal 530 may perform datatransmission and reception with the relay terminal 520 through datarelaying using the first and fourth RAP layers 513 and 533 when normaldata transmission and reception is impossible through a Uu access link.Then, data transmission/reception between the base station 510 and theremote terminal 530 may be relayed using the second RAP layer 521-1 andthe third RAP layer 521-2 of the relay terminal 520. To this end, theplurality of RAP layers 513, 521-1, 521-2, and 533 may perform functionsof registering, changing, and releasing routing information for datatransmission and reception between the base station 510 and the remoteterminal 530.

In such the situation, when the remote terminal 530 enters acommunication disconnected state and direct data communication with thebase station 510 using a Uu access link is impossible, the remoteterminal 530 may perform data communication with the base station 510through the relay terminal 520 capable of communicating with the basestation 510 using the Uu access link 540.

FIG. 6 is a block diagram illustrating a first exemplary embodiment ofentities of a terminal relay system.

Referring to FIG. 6 , a structure of entities of the terminal relaysystem may include an entity structure 610 for remote terminals and anentity structure 620 for relay terminals in a base station 600. Here, aremote terminal 640 may also support a relay function. Here, the entitystructure 610 for remote terminals in the base station 600 may include aplurality of remote terminal (rUE) PDCP entities 611, a rUE RAP entity612, a plurality of rUE RLC entities 613 not associated with the RAPentity 612, and a plurality of rUE RLC entities 614 associated with theRAP entity 612. In addition, the entity structure 620 for relayterminals in the base station 600 may include a plurality of relayterminal (RUE) PDCP entities 621, a RUE RAP entity 622, a plurality ofRUE RLC entities 623 not associated with the RAP entity 622, and aplurality of RUE RLC entities 624 associated with the RAP entity 622.

As described above, the base station 600 may configure the RAP entities612 and 622 when initial connection configuration with the terminals 640and 650 is completed. That is, the base station 600 may configure theRAP entities 612 and 622 for the respective terminals 640 and 650 whenthe initial connection configuration with all the terminals 640 and 650supporting the relay function is completed. In this case, the basestation 600 may control the terminals 640 and 650 so that the terminals640 and 650 may configure the RAP entities and the RLC entitiesassociated with the RAP entities. Then, when the remote terminal 640enters a communication disconnected state and a relay connection isconfigured using the relay terminal 650, the base station 600 mayconnect the rUE RAP entity 612 and the RUE RAP entity 622 to performrelay data transmission and reception.

Meanwhile, the RAP entities of the RAP layer may perform routing totransmit relay data to a next node or terminal. As such, in order forthe RAP entity to perform routing, relay-related addresses andidentifiers (IDs) for data transmission may be required.

FIG. 7 is a conceptual diagram illustrating a method of assigningaddresses and identifiers to a base station and entities of the basestation.

Referring to FIG. 7 , a structure of entities of the base station mayinclude an entity structure 710 for remote terminals and an entitystructure 720 for relay terminals. Here, the entity structure 710 forremote terminals of the base station 700 may include a plurality of rUEPDCP entities 711, a rUE RAP entity 712, a plurality of rUE RLC entities713 not associated with the rUE RAP entity 712, and a plurality of rUERLC entities 714 associated with rUE RAP entity 712. In addition, theentity structure 720 for relay terminals of the base station 700 mayinclude a plurality of RUE PDCP entities 721, a RUE RAP entity 722, aplurality of RUE RLC entities 723 not associated with the RUE RAP entity722, and a plurality of RUE RLC entities 724 associated with the RUE RAPentity 722.

The base station 700 may have a node address. The node address may beclassified into a root node address and a branch node address accordingto a type of a terminal to which the base station provides acommunication service. Here, a root node address may refer to an addressof a base station in which an RRC and PDCP for a remote terminal areconfigured to provide a communication service to the remote terminal.The remote terminal may receive a node address from the correspondingbase station and configure it as a root node address. In addition, theremote terminal may transmit the root node address to a relay terminal.Meanwhile, a branch node address may refer to a node address of a basestation that provides a communication service to a relay terminalsupporting a Uu access link among relay terminals. The relay terminalmay access the corresponding base station to receive the node addressand configure it as a branch node address. In addition, the relayterminal may transmit the branch node address to the remote terminal.Accordingly, the remote terminal and the relay terminal may determinewhether the root node address and the branch node address are the same.When the root node address and the branch node address are the same, theremote terminal and the relay terminal may determine that the basestation to which the remote terminal was connected before adisconnection of communication is the same as the base station to whichthe relay terminal is connected. On the other hand, when the root nodeaddress and the branch node address are different, the remote terminaland the relay terminal may determine that the base station to which theremote terminal was connected before a disconnection of communication isdifferent from the base station to which the relay terminal isconnected.

The base station 700 may assign a RAP entity ID to each of the RAPentities 712 and 722. That is, the base station 700 may assign a rUE RAPentity ID to the rUE RAP entity 712, and may assign a RUE RAP entity IDto the RUE RAP entity 722. As such, the base station 700 may assigndifferent RAP entity IDs to the rUE RAP entity 712 and the RUE RAPentity 722. Accordingly, the base station 700 may identify the remoteterminal using the root node address and the rUE RAP entity ID.Similarly, the base station may identify the relay terminal using thebranch node address and the RUE RAP entity ID.

The base station 710 may configure the RUE PDCP entity 721 and the RUERLC entity 724 when the relay terminal completes connectionconfiguration through the Uu access link. The base station 710 maydeliver root node address information, RAP entity ID information, andthe like to the relay terminal through a control message, etc. The relayterminal receiving the information may configure the RAP entity and theRLC entity, and store the information on the root node address, RAPentity ID, and the like.

FIG. 8 is a sequence chart illustrating a first exemplary embodiment ofa method for configuring a link between a remote terminal and a basestation.

Referring to FIG. 8 , in the method for configuring a link between aremote terminal and a base station, if the remote terminal is connectedto the base station before a communication service with the base stationis disconnected, the base station may transmit to the remote terminal anRRC reconfiguration message including a relay radio network temporaryidentifier (RNTI), a node address, a RAP entity ID, and the like (S810).As such, the remote terminal may receive the RRC reconfiguration messageincluding the relay RNTI, node address, RAP entity ID, and the like fromthe base station, store the information, and transmit an RRCreconfiguration complete message to the base station in response thereto(S820). In this case, the remote terminal may configure the node addressreceived from the base station as a root node address.

Meanwhile, when the remote terminal enters a communication disconnectedstate in which data transmission and reception cannot be performedthrough a Uu access link due to an obstacle or the like, the remoteterminal may configure a sidelink or relay link with an adjacentterminal.

FIG. 9 is a sequence chart illustrating a first exemplary embodiment ofa method for configuring a link between a remote terminal and a relayterminal.

Referring to FIG. 9 , in the method for configuring a link between aremote terminal and a relay terminal, if the remote terminal enters acommunication disconnected state in which data transmission andreception cannot be performed with the base station through the Uuaccess link due to an obstacle or the like, the remote terminal maytransmit a link configuration request message to the relay terminal inorder to configure a side link or a relay link with the relay terminal(S910). Then, in response to the link configuration request message, therelay terminal may transmit a link configuration response messageincluding a node address of a currently connected base station to theremote terminal (S920). Accordingly, the remote terminal may configurethe node address included in the link configuration response messagereceived from the relay terminal as a branch node address, and maytransmit a link configuration complete message to the relay terminal(S930). Through this process, an RRC entity of the remote terminal mayperform link switching from the Uu access link to the relay link whenthe configuration of the side link or the relay link is completed.

FIG. 10 is a sequence chart illustrating a first exemplary embodiment ofa method for switching a link with a remote terminal from a Uu accesslink to a relay link.

Referring to FIG. 10 , in the method for switching a link with a remoteterminal from a Uu access link to a relay link, an RRC entity of theremote terminal may configure a link switching request message anddeliver it to a RAP entity when configuration of the relay link iscompleted (S1010). A process in which the RRC entity of the remoteterminal configures the link switching request message and transmits itto the relay terminal may be described in detail with reference to FIG.11 as follows.

FIG. 11 is a flowchart illustrating a first exemplary embodiment of anoperation method of an RRC entity of a remote terminal.

Referring to FIG. 11 , in the operation method of an RRC entity of aremote terminal, the RRC entity of the remote terminal may generate amessage authentication code for integrity (MAC-I) by processingintegrity protection based on the relay RNTI, root node address, RAPentity ID, and the like when the configuration of the relay link iscompleted (S1011). In addition, the RRC entity may configure the linkswitching request message including the relay RNTI, root node address,RAP entity ID, signaling radio bearer 1 (SRB1) uplink (UL) count(COUNT), and MAC-I information (S1012). Then, the RRC entity of theremote terminal may transmit the configured link switching requestmessage to the RAP entity of the remote terminal (S1013). In addition,the RRC entity of the remote terminal may start a link switching timer(e.g., timer Txx) (S1014).

Referring again to FIG. 10 , upon receiving the link switching requestmessage from the RRC entity, the RAP entity of the remote terminal mayconfigure a relay information setup request message by forming a relayinformation setup request control PDU using the relay RNTI, root nodeaddress, RAP entity ID, SRB1 UL count, and MAC-I information of the linkswitching request message. Then, the RAP entity of the remote terminalmay transmit the relay information setup request message to the RAPentity of the relay terminal (S1020-1). Then, the RAP entity of therelay terminal may register the routing information in the relayinformation setup request control PDU included in the relay informationsetup request message to a routing table. Then, the RAP entity of therelay terminal may transmit the received relay information setup requestmessage to a RUE RAP entity of the base station (S1020-2). Meanwhile,the RUE RAP entity of the base station receiving the relay informationsetup request message from the RAP entity of the relay terminal mayregister the routing information in the relay information setup requestcontrol PDU included in the relay information setup request message to arouting table. The RUE RAP entity of the base station may transmit thereceived relay information setup request message to a rUE RAP entity ofthe base station (S1020-3). Accordingly, the rUE RAP entity of the basestation may configure a link switching request message using the relayRNTI, root node address, RAP entity ID, SRB1 UL count, and MAC-Iinformation included in the received relay information setup requestmessage, and deliver it to an RRC entity of the base station (S1030).Then, the RRC entity of the base station may perform integrityprotection on the link switching request message, and perform linkswitching according to the link switching request of the link switchingrequest message when an integrity check on the message is successful(S1040). Then, the RRC entity may generate a link switching messageaccording to the link switching and deliver it to the rUE RAP entity ofthe base station (S1050).

FIG. 12 is a flowchart illustrating a first exemplary embodiment of alink switching method of an RRC entity of a base station.

Referring to FIG. 12 , in the link switching method of the RRC entity ofthe base station, upon receiving the link switching request message, theRRC entity of the base station may identify the remote terminal based onthe relay RNTI included in the received link switching request message(S1041). Then, the RRC entity of the base station may generate a MAC-Ibased on the relay RNTI, root node address, RAP entity ID, and SRB1 ULcount included in the link switching request message (S1042). Then, theRRC entity of the base station may perform integrity check based on thegenerated MAC-I to authenticate validity of the terminal (S1043).Accordingly, the RRC entity of the base station may determine whetherthe integrity check is successful (S1044), and if the integrity checkfails, the RRC entity of the base station may terminate the linkswitching. On the other hand, if the integrity check is successful, theRRC entity of the base station may generate a MAC-I for integrityprotection based on the relay RNTI, root node address, and RAP entity ID(S1045).

In addition, the RRC entity of the base station may generate a linkswitching message including the generated MAC-I, relay RNTI, root nodeaddress, RAP entity ID, and SRB1 downlink (DL) count, and deliver it tothe rUE RAP entity of the base station (S1046). In this case, the RRCentity of the base station may instruct a PDCP entity of the basestation to switch an uplink path from the Uu access link to the relaylink (S1047). According to the request of the RRC entity of the basestation, the PDCP entity may generate a link switching complete messageafter switching the uplink path from the Uu access link to the relaylink and transmit it to the RRC entity of the base station. Accordingly,the RRC entity of the base station may receive the link switchingcomplete message from the PDCP entity of the base station (S1048). Assuch, when the RRC entity of the base station receives the linkswitching complete message from the PDCP entity of the base station, itmay instruct the PDCP entity of the base station to switch a downlinkpath from the Uu access link to the relay link (S1049). Accordingly, thePDCP entity of the base station may switch the downlink path from the Uuaccess link to the relay link.

Referring again to FIG. 10 , upon receiving the link switching messagefrom the RRC entity of the base station, the rUE RAP entity of the basestation may configure a relay information setup control PDU includingthe MAC-I, relay RNTI, root node address, RAP entity ID, and SRB1 DLcount included in the link switching message, generate a relayinformation setup message including the relay information setup controlPDU, and transmit it to the RUE RAP entity of the base station(S1060-1). Accordingly, the RUE RAP entity of the base station maytransmit the relay information setup message received from the rUE RAPentity of the base station to the RAP entity of the relay terminal(S1060-2).

Accordingly, the RAP entity of the relay terminal receiving the relayinformation setup message may activate a routing table entry in whichthe routing information included in the relay information setup controlPDU is stored. Then, the RAP entity of the relay terminal may transmitthe relay information setup message including the relay informationsetup control PDU (S1060-3). Accordingly, the RAP entity of the remoteterminal may receive the relay information setup message from the RAPentity of the relay terminal, generate a link switching messageincluding the MAC-I, relay RNTI, root node address, RAP entity ID, andSRB1 DL count included in the received relay information setup message,and transmit it to the RRC entity of the remote terminal (S1070). Assuch, upon receiving the link switching message, the RRC entity of theremote terminal may perform integrity protection, and if the integritycheck is successful, the RRC entity of the remote terminal may performlink switching by transmitting uplink data through the relay link(S1080).

FIG. 13 is a flowchart illustrating a first exemplary embodiment of alink switching method of an RRC entity of a remote terminal.

Referring to FIG. 13 , in the link switching method of the RRC entity ofthe remote terminal, the RRC entity of the remote terminal may determinewhether the link switching message is received within a waiting time byreferring to the running link switching timer (S1071). As a result ofthe determination, the RRC entity of the remote terminal may stop thelink switching timer if the link switching message is received withinthe waiting time (S1072). In addition, the RRC entity of the remoteterminal may generate a MAC-I based on the relay RNTI, root nodeaddress, RAP entity ID, and SRB1 DL count of the link switching message(S1073). Then, the RRC entity of the remote terminal may performintegrity check by comparing the generated MAC-I with the MAC-I includedin the received link switching message (S1074).

The RRC entity of the remote terminal may determine whether theintegrity check is successful (S1075), and if the integrity check fails,the RRC entity of the remote terminal may terminate the link switching.On the other hand, if the integrity check is successful, the RRC entityof the remote terminal may instruct the PDCP entity of the remoteterminal to switch a path from the Uu access link to the relay link(S1076). Then, the PDCP entity of the remote terminal may switch thepath from the Uu access link to the relay link. On the other hand, ifthe link switching message is not received within the waiting time as aresult of determining whether the link switching message is receivedwithin the waiting time by referring to the running link switchingtimer, the RRC entity of the remote terminal may release the configuredrelay link (S1077), and may perform a process of configuring a new relaylink (S1078).

Referring again to FIG. 10 , after indicating the link switching to thePDCP entity of the remote terminal, the RRC entity of the remoteterminal may generate a link switching complete message, and deliver itto the RRC entity of the base station through the PDCP entity of theremote terminal, RRC entity of the remote terminal, RAP entity of therelay terminal, RUE RAP entity of the base station, rUE RAP entity ofthe base station, and PDCP entity of the base station (S1090).

Meanwhile, when the configuration of the sidelink or the relay link iscompleted, the remote terminal may perform a procedure for configuringthe routing information while performing the link switching process.

FIG. 14 is a flowchart illustrating a first exemplary embodiment of amethod for configuring routing information performed by a remoteterminal.

Referring to FIG. 14 , in the method of configuring routing informationperformed by the remote terminal, the RRC entity of the remote terminalmay deliver to the RAP entity of the remote terminal relay linkconfiguration information including a source layer 2 ID, destinationlayer 2 ID, and the like and relay routing information including theroot node address, the branch node address, the RAP entity ID, and thelike (S1410). Then, the RAP entity of the remote terminal may receivethe root node address, branch node address, RAP entity ID, and the likefrom the RRC entity of the remote terminal, and register them to therouting table (S1420). Thereafter, the RRC entity of the remote terminalmay generate the link switching request message and deliver it to theRAP entity of the remote terminal (S1430). Then, the RAP entity of theremote terminal may form a relay information setup control PDU includingthe link switching request message (S1440), and transmit it to the relayterminal as the relay information setup request message (S1450). Here,the relay information setup request control PDU may include the rootnode address, branch node address, RAP entity ID, and the like as relaylink routing information. Thereafter, when the RAP entity of the remoteterminal receives the relay information setup control PDU including thelink switching message from the relay terminal through the relayinformation setup message (S1460), the RAP entity of the remote terminalmay activate the registered relay link routing information (S1470). Inaddition, the RAP entity of the remote terminal may deliver the linkswitching message included in the relay information setup message to theRRC entity of the remote terminal (S1480). Accordingly, the RRC entityof the remote terminal may perform the link switching.

FIG. 15 is a flowchart illustrating a first exemplary embodiment of amethod for configuring routing information performed by a RAP entity ofa relay terminal.

Referring to FIG. 15 , in the method for the RAP entity of the relayterminal to configure routing information, the RRC entity of the relayterminal may transmit information on the source layer 2 ID anddestination layer 2 ID of the relay link to the RAP entity of the relayterminal when the configuration of the relay link is completed. Then,the RAP entity of the relay terminal may receive the information fromthe RRC entity of the relay terminal, and store the source layer 2 IDand the destination layer 2 ID of the relay link (S1501). In addition,upon receiving the relay information setup request control PDU includingthe root node address, branch node address, RAP entity ID, and the likefrom the RAP entity of the remote terminal by using the stored sourcelayer 2 ID and destination layer 2 ID through the relay informationsetup request message (S1502), the RAP entity of the relay terminal mayconfigure a routing table entry based on the routing information such asthe root node address, branch node address, RAP entity ID, source layer2 ID, destination layer 2 ID, and the like (S1503). Then, the RAP entityof the relay terminal may start a relay information setup timer (e.g.,timer T_s) (S1505) while maintaining the configured routing table entryin an inactive state (S1504). In addition, the RAP entity of the relayterminal may forward the relay information setup request control PDU tothe base station through the relay information setup request message(S1506).

Thereafter, the RAP entity of the relay terminal may determine whetherthe relay information setup control PDU is received from the basestation through the relay information setup message within a relay setuptime by referring to the relay information setup timer (S1507). As aresult of the determination, if the RAP entity of the relay terminalreceives the relay information setup control PDU from the base stationwithin the relay setup time, the RAP entity of the relay terminal maysearch for a routing table entry based on the root node address, branchnode address, and RAP entity ID included in the relay information setupcontrol PDU (S1508). When a routing table entry is retrieved, the RAPentity of the relay terminal may switch the retrieved routing tableentry to an active state (S1510), and may stop the relay informationsetup timer (S1511). Then, the RAP entity of the relay terminal maytransmit the received relay information setup control PDU to the remoteterminal through the relay information setup message (S1512). If arouting table entry is not retrieved in the routing table, the RAPentity of the relay terminal may delete the received relay informationsetup control PDU (S1513). On the other hand, the RAP entity of therelay terminal may delete the associated routing table entry if therelay information setup control PDU is not received within the relaysetup time by referring to the relay information setup timer (S1514).

FIG. 16 is a flowchart illustrating a first exemplary embodiment of amethod for data relaying performed by a relay terminal.

Referring to FIG. 16 , in the method for data relaying performed by therelay terminal, the RAP entity of the relay terminal may activate therouting table entry (S1601) and may start a data reception timer (e.g.,T_a) (S1602). The RAP entity of the relay terminal may determine whetherdata is received within a data reception time by referring to the datareception timer (S1603). If data is received within the data receptiontime, the RAP entity of the relay terminal may search for a routingtable entry based on the root node address, branch node address, and RAPentity ID included in the received data (S1604). The RAP entity of therelay terminal may determine whether a matched routing table entry isretrieved (S1605), and if a matched routing table entry is retrieved,the RAP entity of the relay terminal may transmit the data to thecorresponding base station based on the retrieved routing table entry(S1606). In addition, the RAP entity of the relay terminal may restartthe data reception timer (S1607). If a matched routing table entry isnot found in the routing table, the RAP entity of the relay terminal maydelete the received data (S1608). On the other hand, the RAP entity ofthe relay terminal may delete the routing table entry associated withthe data reception timer if data is not received within the datareception time by referring to the data reception timer (S1609). Inaddition, the RAP entity of the relay terminal may release the routinginformation associated with the relay link if there is no routing tableentry associated with the relay link (S1610), and may notify the RRCentity of the relay terminal of such the release (S1611).

FIG. 17 is a conceptual diagram illustrating a third exemplaryembodiment of a terminal relay system.

Referring to FIG. 17 , a terminal relay system may include a first basestation 1711, a second base station 1712, a first terminal 1721, and asecond terminal 1722. The first terminal 1721 and the second terminal1722 may be located in a communication service coverage of the firstbase station 1711. As such, since the first terminal 1721 is located inthe communication service coverage of the first base station 1711, thefirst terminal 1721 may directly access the first base station 1711 totransmit and receive data to and from the first base station 1711. Inaddition, since the second terminal 1722 is located in the communicationservice coverage of the second base station 1712, the second terminal1722 may directly access the second base station 1712 to transmit andreceive data to and from the second base station 1712. From such thestate, the first terminal 1721 may enter a communication disconnectedstate in which data cannot be transmitted and received to and from thefirst base station 1711 due to an obstacle or the like. In this case,the first terminal 1721 may access the first base station 1711 via thesecond terminal 1722 to transmit and receive data to and from the firstbase station 1711. In this case, the second terminal 1722 may relaycommunication between the first base station 1711 and the first terminal1721.

Meanwhile, in such the situation, the second terminal 1722 may move to acommunication service coverage of the second base station 1712 byhandover or the like. In this case, since the second terminal 1722 islocated in the communication service coverage of the second base station1712, the second terminal 1722 may access the second base station 1712to transmit and receive data to and from the second base station 1712.In such the state, the first terminal 1721 may transmit and receive datato and from the first base station 1711 via the second base station 1712through the second terminal 1722. In this case, the second terminal 1722may relay communication between the second base station 1712 and thefirst terminal 1721. In addition, the second base station 1712 may relaycommunication between the first base station 1711 and the secondterminal 1722.

As described above, when the second terminal 1712 moves from thecommunication service coverage of the first base station 1711 to thecommunication service coverage of the second base station 1712 due to ahandover or the like, a change in the branch node address may berequired. In this case, the second terminal 1722 may transmit a relayinformation change indication message to the first terminal 1721 toinform the first terminal 1721 that the branch node address has beenchanged. Here, the relay information change indication message mayinclude the changed new branch node address.

FIG. 18 is a flowchart illustrating a first exemplary embodiment of amethod of changing a branch node address performed by a relay terminal.

Referring to FIG. 18 , in the method for the relay terminal to changethe branch node address, the RAP entity of the relay terminal mayidentify whether the branch node address is changed according tointer-cell movement (S1801). As a result of identifying whether thebranch node address is changed, if the branch node address is changed,the RAP entity of the relay terminal may configure a new routing tableentry by reflecting the new branch node address to the root node addressand RAP entity ID of the previous routing table entry (S1802). Then, theRAP entity of the relay terminal may start a routing information updatetimer (e.g., timer T_a) associated with the new routing table entry(S1803).

Thereafter, the RAP entity of the relay terminal may generate andtransmit a relay information change indication message through the relaylink in order to notify remote terminals connected to the relay link ofthe change in the branch node address (S1804). Then, the RAP entity ofthe relay terminal may delete the previous routing table entry if therouting information update timer expires by referring to the routinginformation update timer (S1805).

FIG. 19 is a flowchart illustrating a first exemplary embodiment of amethod for changing a branch node address performed by a remoteterminal.

Referring to FIG. 19 , in the method of changing the branch node addressperformed by the remote terminal, upon receiving the relay informationchange indication message from the relay terminal (S1901), the RAPentity of the remote terminal may generate and add a new routing tableentry reflecting the new branch node address to the root node addressand the RAP entity ID of the previous routing table entry to the routingtable (S1902). In addition, the RAP entity of the remote terminal maystart a routing information update timer (e.g., timer T_a) associatedwith the routing table entry added to the routing table (S1903). Then,the RAP entity of the remote terminal may transmit a PDU using the newbranch node address (S1904). In addition, the RAP entity of the remoteterminal may delete the previous routing table entry when the routinginformation update timer expires by referring to the routing informationupdate timer (S1905).

The exemplary embodiments of the present disclosure may be implementedas program instructions executable by a variety of computers andrecorded on a computer readable medium. The computer readable medium mayinclude a program instruction, a data file, a data structure, or acombination thereof. The program instructions recorded on the computerreadable medium may be designed and configured specifically for thepresent disclosure or can be publicly known and available to those whoare skilled in the field of computer software.

Examples of the computer readable medium may include a hardware devicesuch as ROM, RAM, and flash memory, which are specifically configured tostore and execute the program instructions. Examples of the programinstructions include machine codes made by, for example, a compiler, aswell as high-level language codes executable by a computer, using aninterpreter. The above exemplary hardware device can be configured tooperate as at least one software module in order to perform theembodiments of the present disclosure, and vice versa.

While the embodiments of the present disclosure and their advantageshave been described in detail, it should be understood that variouschanges, substitutions and alterations may be made herein withoutdeparting from the scope of the present disclosure.

What is claimed is:
 1. An operation method of a first terminal in acommunication system, the operation method comprising: configuring a Uuaccess link with a base station, and receiving a first message from thebase station, the first message including a relay radio networktemporary identifier (RNTI) for identifying the first terminal, a nodeaddress of the base station, and a relay adaptation protocol (RAP)entity identifier (ID) for identifying a RAP entity configured for thefirst terminal; configuring a relay link with a second terminal whencommunication with the base station is disconnected; requesting linkswitching by transmitting to the base station a second message via thesecond terminal, the second message including the relay RNTI, the nodeaddress, and the RAP entity ID; and receiving a response to the secondmessage from the base station via the second terminal, and switching alink with the base station from the Uu access link to the relay link. 2.The operation method according to claim 1, wherein the requesting of thelink switching comprises: generating a first message authentication codefor integrity (MAC-I) by processing integrity protection based on therelay RNTI, the node address, and the RAP entity; generating the secondmessage including the relay RNTI, the node address, the RAP entity, andthe first MAC-I information; and requesting the link switching bytransmitting the second message to the base station via the secondterminal.
 3. The operation method according to claim 1, wherein thereceiving of the response and the switching of the link comprises:receiving the response to the second message including the relay RNTI,the node address, and a second MAC-I from the base station via thesecond terminal; generating a third MAC-I by processing integrityprotection based on the relay RNTI and the node address; and in responseto determining that the third MAC-I and the second MAC-I match,switching the link with the base station from the Uu access link to therelay link, and transmitting uplink data through the relay link.
 4. Theoperation method according to claim 1, further comprising, after theconfiguring of the relay link, configuring a routing table entry basedon the node address, the RAP entity ID, and a first branch node addressreceived from the second terminal in the configuring of the relay link;and in response to receiving the response to the second message from thebase station, activating the routing table entry.
 5. The operationmethod according to claim 4, further comprising: receiving, from thesecond terminal, a third message requesting update of the routing tableentry, the third message including a second branch node address; andupdating the routing table entry by reflecting the second branch nodeaddress.
 6. The operation method according to claim 1, furthercomprising: starting a timer after transmitting the second message; andreleasing the relay link if the response to the second message is notreceived within a waiting time defined by the timer.